Existing railroad locomotives are typically powered by a diesel engine or engines which utilize an alternator to deliver electric power to traction motors which in turn power the drive wheels of the locomotive.
As described in U.S. Pat. No. 6,208,097, when a locomotive accelerates, the traction motors apply torque to the driving axles which is converted to tractive effort of the wheels on the rails. When braking, an air brake system and often the motors themselves, may be used to apply a braking force on the rails.
Maximum tractive or braking effort is achieved if each of the driving axles is rotating such that its actual tangential speed is slightly higher while accelerating or slightly lower when braking than the true ground speed of the locomotive. If adhesion is reduced or lost, some or all of the driving wheels may experience slip while accelerating or skid while braking. Excessive wheel slip or wheel skid can lead to accelerated wheel wear, rail damage, high mechanical stresses in the drive components of the propulsion system, and an undesirable decrease of the desire tractive or braking effort.
Various methods of detection of wheel slip and wheel skid are known and are discussed, for example, in U.S. Pat. No. 5,610,819, U.S. Pat. No. 6,208,097 and U.S. Pat. No. 6,012,011. These methods include measurement of traction motor current, traction motor rpm and the use of tachometers on the driving axles.
Without an accurate measurement of true locomotive velocity or acceleration, wheel slip and skid detection systems cannot readily detect synchronous wheel slip or skid. The most common method of measuring true locomotive velocity is the use of ground speed radar. These systems are costly, have reliability problems (the radar system needs to be exposed to the elements and subject to damage) and have difficulties in certain weather conditions (snow buildup for example can interfere with radar speed readings).
Other prior art systems known to the Applicant are described in the following documents: U.S. Pat. No. 1,377,087, U.S. Pat. No. 6,308,639, U.S. patent application Ser. No. 10/083,587, U.S. patent application Ser. No. 10/649,286, U.S. Pat. No. 6,208,097, U.S. Pat. No. 6,012,011, U.S. Pat. No. 3,982,164, U.S. Pat. No. 4,035,698, U.S. Pat. No. 4,070,562, U.S. Pat. No. 4,075,538, U.S. Pat. No. 4,095,147, U.S. Pat. No. 4,344,139, U.S. Pat. No. 4,347,569, U.S. Pat. No. 4,701,682, U.S. Pat. No. 4,799,161, U.S. Pat. No. 4,936,610, U.S. Pat. No. 4,941,099, U.S. Pat. No. 4,944,539, U.S. Pat. No. 4,950,964, U.S. Pat. No. 5,289,093, U.S. Pat. No. 5,428,538, U.S. Pat. No. 5,436,538, U.S. Pat. No. 5,610,819, U.S. Pat. No. 6,208,097, U.S. Pat. No. 5,129,328, U.S. Pat. No. 4,900,944, U.S. Pat. No. 6,615,118, U.S. Pat. No. 7,084,602, U.S. Pat. No. 7,064,507, U.S. application Ser. No. 11/060,087.
Thus, there remains a need for a reliable, low cost, all-weather means of determining true locomotive speed which is a key variable for determining the occurrence of synchronous wheel slip or skid and for determining an accurate value of each wheels amount of slip or skid. These and other needs are addressed by the various embodiments and configurations of the present invention which are directed generally to use of an acceleration based system to determine true locomotive kinetic acceleration and hence speed which, in turn, will allow detection and quantitative calculation of all modes of wheel slip and skid.